1. Field of the Invention
The present invention relates to a line start permanent magnet motor, and more particularly, to a rotor of a line start permanent magnet motor capable of reducing a rotor resistance of a rotor, thus improving a synchronization performance, and simplifying an assembly process and a manufacturing method thereof.
2. Description of the Conventional Art
Generally, an induction motor has an operational principle that a current is applied to a coil wound at an inner portion of a stator thus to generate a rotation magnetic field and thereby an electromotive force is induced to a rotor rotatably inserted into inside of the stator thus to rotate the rotor.
Meanwhile, a line start permanent magnet motor has a structure that a permanent magnet is inserted into to a rotor constituting the induction motor. The line start permanent magnet motor is operated by a torque generated by an interaction between a secondary current generated by a voltage generated at the rotor at the time of driving and a magnetic flux generated by a winding coil of the stator. At this time, the torque is operated by composing a torque component by a rotor cage, a reluctance torque component, and a component by a permanent magnet.
Then, at the time of a rated operation after starting, a flux of the permanent magnet coupled to the rotor and a flux generated from the stator are reciprocally synchronized, so that the rotor is operated as a rotation magnetic field speed of the stator. At this time, most of the torque is the permanent magnet torque component.
The line start permanent magnet motor can be at once started as a supply voltage without using an additional position sensor or a drive. Also, since an excited current is not required differently from the induction motor and current does not flow into the rotor cage at a synchronous speed, a secondary eddy current loss can be reduced thus to enhance efficiency than other motors.
Meanwhile, the line start permanent magnet motor serves as a rotation resistance at the time of rotation according to a structure of the rotor thus to influence to the rotor torque, thereby lowering a synchronization performance thereof.
FIG. 1 is a sectional view showing a rotor of a line start permanent magnet motor in accordance with the conventional art, FIG. 2 is a left sectional view of the rotor of a line start permanent magnet motor in accordance with the conventional art, and FIG. 3 is a right sectional view of the rotor of a line start permanent magnet motor in accordance with the conventional art. As shown, the rotor of a line start permanent magnet motor is composed of a first end ring 20 and a second end ring 30 asymmetrically formed at both sides of a stacked core 10 to inside thereof an shaft is coupled, and the first and second end rings 20 and 30 are connected to each other by a plurality of connecting portions 21 penetrating the stacked core 10. The stacked core 10 is constituted with a cylindrical body 11 of a cylindrical shape having a constant length; an axial hole 12 formed in the middle of the cylindrical body 11 for inserting an shaft; a plurality of first penetration holes 13 formed at an edge of the cylindrical body 11 for inserting the connecting portions 21; and a plurality of second penetration holes 14 and quadrangular penetration holes 15 formed in the cylindrical body 11. The stacked core 10 is a stacked body that a plurality of thin plates having a constant thickness are stacked.
The first end ring 20 is provided with a rivet portion 23 formed at one side of a ring-shaped body portion 22 of a ring shape having a constant thickness and respectively inserted into the second penetration holes 14, and the second end ring 30 is provided with insertion penetration holes 32 of a hexagon shape of a non-circular shape formed in a ring-shaped body portion 31 having a constant thickness. The ring-shaped body portion 22 of the first end ring and the ring-shaped body portion 31 of the second end ring are connected to each other by the connecting portions 21.
The stacked core 10, the first end ring 20, and the second end ring 30 constitute one circuit.
Also, permanent magnets 40 are penetratingly inserted into the quadrangular penetration holes 15 of the stacked core 10, and the permanent magnets 40 are arranged in a state that two permanent magnets are facing each other, respectively.
A supporting plate 50 for supporting the permanent magnets 40 is coupled between the first end ring 20 and the stacked core 10, and a covering plate 60 for covering the permanent magnets 40 is inserted into the second end ring 30 thus to be coupled to one side surface of the stacked core 10. The supporting plate 50 is formed with a constant thickness and as a corresponding shape to one side surface of the stacked core 10, in which the quadrangular penetration holes 15 were excluded. The covering plate 60 of a hexagon shape for covering the permanent magnets 40 is provided with an axial hole 61 formed in the middle thereof, and a rivet hole 62 formed at both sides of the axial hole 61. The covering plate 60 is fixedly coupled by inserting the rivet hole 62 of the covering plate into the rivet portion 23 of the first end ring in a state that the covering plate 60 is inserted into the insertion penetration holes 32 of the second end ring 30.
Manufacturing processes for the rotor of a line start permanent magnet motor will be explained as follows.
FIG. 4 is a flow chart showing a manufacturing method of the rotor of a line start permanent magnet motor in accordance with the conventional art. As shown, the method comprises the steps of: stacking thin plates constituting the stacked core 10 and thereby manufacturing the stacked core 10; coupling the supporting plate 50 to one side surface of the stacked core 10, performing Al die casting on the stacked core 10, and thereby forming the first and second end rings 20 and 30, in which Al is not introduced into the quadrangular penetration holes 15 of the stacked core 10 by the supporting plate 50; respectively inserting permanent magnets 40 into the quadrangular penetration holes 15 of the stacked core 10 through the insertion penetration holes 32 of the second end ring; inserting the covering plate 60 into the insertion penetration holes 32 of the second end ring and thereby covering the permanent magnets 40, in which the rivet hole 62 of the covering plate is inserted into the rivet portion 23 of the first end ring; and riveting the rivet portion 23 and thereby fixing the covering plate 60.
The rotor manufactured by said processes is rotatably inserted into the stator constituting the line start permanent magnet motor, and the shaft is fixedly coupled to the axial hole 12 of the rotor.
The rotor of the line start permanent magnet motor is rotated by the aforementioned electromagnetic operation according to an operation of the line start permanent magnet motor, thereby transmitting a rotational force to another system through the shaft.
However, in the rotor of the line start permanent magnet motor, since the second end ring 30 coupled to one side of the stacked core 10 is formed as a shape that the permanent magnets 40 and the covering plate 60 can be penetratingly inserted, the second end ring 30 is formed asymmetrically and a shape of the second end ring 30 is different from a shape of the first end ring 20 thus to generate a rotation imbalance when the rotor is rotated. Also, by a shape of the insertion penetration holes 32 of the second end ring 30, a sectional area of the second end ring 30 becomes small, thereby increasing a secondary resistance and thus lowering a synchronization performance. Additionally, since the covering plate 60 for covering the permanent magnets 40 is coupled by the riveting, an assembly structure becomes complicated thus to lower an assembly productivity.